Polyethylene resins are used to prepare food packaging films, grocery bags, stretch-wrap films, shrink-wrap films, garbage can liners and shipping bags. Some applications, such as wrapping raw or prepared food, require films that have low water vapor and oxygen transmission rates to preserve the contents.
Packaging films with low water vapor transmission rates (WVTR) and low oxygen transmission rates (OTR) are generally produced using laminating foil, metalized films (e.g., aluminum on poly(ethylene terephthalate) or polyethylene), or through the use of metal oxides (e.g., silicon dioxide (SiO2), titanium oxide (TiO2) or aluminum oxide (Al2O3)), which can be deposited by chemical vapor deposition. The addition of metalized films or metal oxides increases the cost and complexity of producing these films. Polyvinylidene chloride laminated films are also commonly used because of their excellent barrier properties. Although these laminated films have low WVTR and OTR, they tend to be more expensive to produce than polyolefin films.
Multilayer barrier films are also widely used in the packaging industry. Depending on the intended end-use of the film, the number and arrangement of the various layers as well as the types of polymer resins employed will vary. Polymer resins used include a wide variety of polar and non-polar polymers selected for their ability to provide essential properties such as structural integrity, puncture resistance, abrasion resistance, etc. Resins having barrier properties are generally included as a barrier layer to prevent the passage of oxygen and moisture in multi-layer constructions used for food packaging. Commonly used barrier resins for these applications include ethylene-vinyl alcohol (EVOH) copolymers, nylons and the like. Barrier resins usually cost more than polyethylene resins. In addition, multilayer films are made by complex coextrusion processes.
Improving the barrier properties of polyethylene films is of great interest because the improved polyethylene films can be used alone as barrier films or they can be used as layers in multilayer films to improve the overall barrier properties of the multilayer films.